Personal care articles, such as infant and feminine care products are typically composed of multiple components including the cover (also known as topsheet or liner), absorbent layer(s) and baffle. The topsheet in conjunction with the absorbent layer(s) must deliver softness and comfort, protection, good absorbency and liquid intake properties, dryness, visual distinctiveness and cleanliness. The extent to which these traits are met is dependent on the interaction of a bodily fluid with the structure and surface chemistry of the cover and absorbent as well as the interface between adjacent or interconnected materials.
Two cover approaches have typically been pursued to attain the desired features: apertured film covers and nonwoven covers. Nonwoven materials are soft and comfortable but often lack the required functional attributes (clean, dry, and absorbent) while apertured film covers can deliver the required functionality but are generally hot, plasticky, and uncomfortable.
A number of apertured film covers have been described in the patent art. These vary widely in their functional performance. Several main categories of film covers are known based on their structure and the methods of manufacture. For instance, two dimensional film covers (using a slit and stretch aperture method) were developed by Hovis et al. (U.S. Pat. No. 5,262,107). Due to their structure, these apertured films have relatively slow intake rates and high rewet and staining compared to other apertured films. Three dimensional apertured film covers were described by Thompson et. al. (U.S. Pat. No. 3,929,135) and others using both vacuum aperturing and pin aperturing. These materials have relatively rapid intake, low rewet, and low staining due to their tailored structure including apertures on the top and bottom surface, depth of aperturing, and tapering of the apertures. Other structures have been created which have some characteristics of both two and three dimensional cover materials. These are often characterized as two dimensional films with appendages or extensions protruding from the bottom surface. They often are produced using pin aperturing techniques.
Nonwovens such as monocomponent spunbond webs often have poor functional performance due to their generally small average pore size, low permeability, and two dimensional nature. Other structures such as crimped conjugate spunbond webs and through air bonded carded webs can be three dimensional but also tend to have low permeability and small average pore size. The permeability and pore size may be increased through, for example, increased fiber denier and decreased basis weight, but at the extreme limits, softness and other aesthetic features can be compromised. Additionally, under these conditions one often sees a tradeoff in properties; for example, such than intake rate increases with increase in permeability, but rewet and staining may also increase.
Integrated composite structures are also described in the art and include apertured film/nonwoven laminates and nonwoven/nonwoven laminates. These structures often deliver improvements in functional performance and softness, however, these structures are often more expensive due to their increased complexity and the incorporation of multiple layers of materials.
The cover is sometimes referred to as a body side liner or topsheet when referring to diapers, and is usually adjacent a surge material. In the thickness direction of the article, the liner material is the layer against the wearer's skin and so the first layer in contact with liquid or other exudate from the wearer. The liner further serves to isolate the wearer's skin from the liquids held in an absorbent structure and should be compliant, soft feeling and non-irritating.
A properly functioning diaper body side liner should have good intake properties so that the incoming liquid stream is transported through the material completely and hence, minimal pooling and spreading of the liquid at the surface occurs. Pooling and spreading at the surface can contribute to leakage and increase skin hydration or wetness. Additionally, the body side surface of the liner should have minimal saturation so that skin hydration does not increase. It is desirable that personal care articles be designed so as to minimize skin hydration since its believed to contribute to the occurrence of diaper rash. If the liner has poor liquid intake qualities and remains saturated, or has fluid spreading properties, skin hydration will be increased.
There remains a need for a material which delivers the desired functional attributes of cleanliness, dryness and absorbency in one material, while still maintaining the softness and comfort normally associated with fibrous nonwoven webs. It is one object of this invention to provide such a material.